*I agree that the sort of cycling you've described is poor but if you look at the highway code, the overtaking example shown in the photo shows the car in the opposing lane. This swerving is really no different than being blown sideways by a strong wind.
But ultimately if you can read the road then it is quite obvious what other road users are going to do. If not then perhaps an advanced driving course would be appropriate.*
That is just so typical of the arrogant, entitled attitude which causes bad feeling between cyclists and car drivers in the first place.
The three men concern were behaving irresponsibly and dangerously in lane one of a dual carriageway while other vehicles were, quite reasonably, overtaking them. The cyclists were racing and started swerving into lane two despite the presence of another vehicle and it is the driver of the other vehicle who should be patronised and advised to improve their driving skills.
These cyclists should not have been racing and trying to stop each other overtaking. Had they been taking a sensible line down the centre of lane one, checking over their shoulders and overtaking each other in a safe and sensible manner, when there was a gap in lane two, as befits any road user, nobody need have been put at risk.
Are you suggesting that nobody should overtake cyclists on a dual carriageway just in case they start overtaking each other without looking and swerving into the path of another vehicle? That could make for some enormous, very slow moving tailbacks.
Why not just behave responsibly with due consideration for other road users? That is what I was doing.